Saccharomyces cerevisiae can utilize allantoin as sole nitrogen source by degrading it in five steps to ammonia, glyoxylate, and CO2. The enzymes of this pathway are inducible; allophanate, the last intermediate of the pathway, is the inducer. We have demonstrated control of induction occurs at the level of transcription. In order to study the mechanisms underlying control of gene expression with respect to this pathway, a search will be mounted for mutant strains defective in the control elements of the pathway. Studies will also be performed to determine the genetic characteristics and biochemical consequences of mutations in strains which pleiotropically loose the ability to complement urea carboxylase and allophanate hydrolase defective strains.